Metabolic Regulation of Mesophilic Methanosarcina barkeri to Ammonium Inhibition

Overcoming Extreme Ammonia Inhibition on Methanogenesis by Artificially Constructing a Synergistically Community with Acidogenic Bacteria and Hydrogenotrophic Archaea

High total ammonia nitrogen (TAN) inhibits anaerobic digestion (AD) and cannot be completely eliminated by merely enhancing a stage of AD. This study incorporates TAN-tolerant inoculum into substrates hydrolyzed by Rhizopus mixed agents to simultaneously enhance hydrolysis-acidogenesis-methanogenesis. The results show a 16.46-fold increase in CH4 production under TAN-inhibited (6870.97 mg L-1) conditions, even exceeding the AD without TAN by 21.10%. Model substrates sodium acetate and mixed H2 confirm hydrogenotrophic methanogenesis is the main pathway, with reduced TAN inhibition. Furthermore, a synergistic metabolic microbial community dominated by hydrolytic bacteria JAAYGG01 sp. and DTU014 sp., acidogenic bacteria DTU015 sp., DTU013 sp., and JAAYLO01 sp., and methanogens Methanosarcina mazei and an unclassified species in the Methanoculleus is reconstructed to resist TAN inhibition. Metagenomic combined with metatranscriptomic sequencing identifies that this microbial community carries xynD and bglB to regulate substrate hydrolysis, leading to acetate production through glycolysis, butyrate, and pyruvate metabolism with high acetate kinase activity, thereby CH4 produced primarily via hydrogenotrophic methanogenesis with high coenzyme F420 activity, facilitated by efficient mass transfer processes and quorum sensing regulation. This cleaner strategy obtains higher economic benefit (US$149.02) than conventional AD and can increase 154.64-fold energy production of a 24 000 m3 biogas plant, guided by machine learning.

Deciphering the function of Fe3O4 in alleviating propionate inhibition during high-solids anaerobic digestion: Insights of physiological response and energy conservation

Fe3O4 is a recognized addictive to enhance low solid anaerobic digestion (AD), while for high solid AD challenged by acidity inhibition, its feasibility and mechanism remain unclear. In this study, the positive effect of Fe3O4 on high-solids AD of food waste by regulating microbial physiology and energy conservation to enhance mutualistic propionate methanation was documented. The methane yield was increased by 36.7 % with Fe3O4, which because Fe3O4 alleviated propionate stress on methane generation, along with improved propionate degradation and methanogenic metabolism. Fe3O4 facilitated the production of extracellular polymeric substances and the formation of tightly bio-aggregates, fostering an enriched microbial population (e.g., Smithella and Methanosaeta) to resist propionate stress. Also, Fe3O4 up-regulated the genes in stress defense system, cytomembrane biosynthesis/function, metal irons transporter, cell division and enzyme synthesis, verifying its superiority on cellular physiology. In addition, energy-conservation strategies related to intracellular and extracellular electron transfer were enhanced by Fe3O4. Specifically, the enzyme expressions involved in reversed electron transfer and electron bifurcation coupled with direct interspecies electron transfer (DIET) were upregulated by at least 2.2 times with Fe3O4, providing sufficient energy to drive thermodynamic adverse methanogenesis from propionate-stressed condition. Consequently, the reinforced enzyme expression in the dismutation and DIET pathway make it to be the predominant drivers for enhanced methanogenic propionate metabolism. This study fills the knowledge gaps of Fe3O4-induced microbial physiological and energetic strategies to resist environmental stress, and has remarkable practical implicated for restoring inhibited bioactivities.

Different bioaugmentation regimes that mitigate ammonium/salt inhibition in repeated batch anaerobic digestion: Generic converging trend of microbial communities

Bioaugmentation regimes (i.e., dosage, repetition, and timing) in AD must be optimized to ensure their effectiveness. Although previous studies have investigated these aspects, most have focused exclusively on short-term effects, with some reporting conflicting conclusions. Here, AD experiments of three consecutive repeated batches were conducted to determine the effect of bioaugmentation regimes under ammonium/salt inhibition conditions. A positive correlation between reactor performance and inoculum dosage was confirmed in the first batch, which diminished in subsequent batches for both inhibitors. Moreover, a diminishing marginal effect was observed with repeated inoculum introduction. While the bacterial community largely influenced the reactor performance, the archaeal community exhibited only a minor impact. Prediction of the key enzyme abundances suggested an overall decline in different AD steps. Overall, repeated batch experiments revealed that a homogeneous bacterial community deteriorated the AD process during long-term operation. Thus, a balanced bacterial community is key for efficient methane production.

Decoding Microbial Responses to Ammonia Shock Loads in Biogas Reactors through Metagenomics and Metatranscriptomics

The presence of elevated ammonia levels is widely recognized as a significant contributor to process inhibition in biogas production, posing a common challenge for biogas plant operators. The present study employed a combination of biochemical, genome-centric metagenomic and metatranscriptomic data to investigate the response of the biogas microbiome to two shock loads induced by single pulses of elevated ammonia concentrations (i.e., 1.5 g NH4+/LR and 5 g NH4+/LR). The analysis revealed a microbial community of high complexity consisting of 364 Metagenome Assembled Genomes (MAGs). The hydrogenotrophic pathway was the primary route for methane production during the entire experiment, confirming its efficiency even at high ammonia concentrations. Additionally, metatranscriptomic analysis uncovered a metabolic shift in the methanogens Methanothrix sp. MA6 and Methanosarcina flavescens MX5, which switched their metabolism from the acetoclastic to the CO2 reduction route during the second shock. Furthermore, multiple genes associated with mechanisms for maintaining osmotic balance in the cell were upregulated, emphasizing the critical role of osmoprotection in the rapid response to the presence of ammonia. Finally, this study offers insights into the transcriptional response of an anaerobic digestion community, specifically focusing on the mechanisms involved in recovering from ammonia-induced stress.

Presence and role of viruses in anaerobic digestion of food waste under environmental variability

BACKGROUND

The interaction among microorganisms in the anaerobic digestion of food waste (ADFW) reactors lead to the degradation of organics and the recycling of energy. Viruses are an important component of the microorganisms involved in ADFW, but are rarely investigated. Furthermore, little is known about how viruses affect methanogenesis.

RESULTS

Thousands of viral sequences were recovered from five full-scale ADFW reactors. Gene-sharing networks indicated that the ADFW samples contained substantial numbers of unexplored anaerobic-specific viruses. Moreover, the viral communities in five full-scale reactors exhibited both commonalities and heterogeneities. The lab-scale dynamic analysis of typical ADFW scenarios suggested that the viruses had similar kinetic characteristics to their prokaryotic hosts. By associating with putative hosts, a majority of the bacteria and archaea phyla were found to be infected by viruses. Viruses may influence prokaryotic ecological niches, and thus methanogenesis, by infecting key functional microorganisms, such as sulfate-reducing bacteria (SRB), syntrophic acetate-oxidizing bacteria (SAOB), and methanogens. Metabolic predictions for the viruses suggested that they may collaborate with hosts at key steps of sulfur and long-chain fatty acid (LCFA) metabolism and could be involved in typical methanogenesis pathways to participate in methane production.

CONCLUSIONS

Our results expanded the diversity of viruses in ADFW systems and suggested two ways that viral manipulated ADFW biochemical processes. Video Abstract.

Thermodynamic restrictions determine ammonia tolerance of methanogenic pathways in Methanosarcina barkeri

Ammonia is a ubiquitous potential inhibitor of anaerobic digestion processes, mainly exhibiting inhibition towards methanogenic activity. However, knowledge as to how ammonia affects the methanogens is still limited. In this study, we cultured a multitrophic methanogen, Methanosarcina barkeri DSM 800, with acetate, H₂/CO₂, and methanol to evaluate the influence of ammonia on different methanogenic pathways. Aceticlastic methanogenesis was more sensitive to increased ammonia concentrations than hydrogenotrophic and methylotrophic methanogenesis. Theoretical maximum NH₃ tolerances of M. barkeri fed with acetate, H₂/CO₂, and methanol were calculated to be 39.1 ± 9.0, 104.3 ± 7.4, and 85.7 ± 1.0 mg/L, respectively. The order of the ΔG range of M. barkeri under three methanogenic pathways reflected the order of ammonia tolerance of M. barkeri. Our results provide insights into the role of the thermodynamic potential of methanogenesis on the tolerance of ammonia stress; and shed light on the mechanism of ammonia inhibition on anaerobic digestion.

Methanogenic treatment of dairy wastewater: A review of current obstacles and new technological perspectives

Methanogenic treatment can effectively manage wastewater in the dairy industry. However, its treatment efficiency and stability are problematic due to the feature of wastewater. This review comprehensively summarizes the dairy wastewater characteristics and reveals the mechanisms and impacts of three critical issues in anaerobic treatment, including ammonia and long-chain fatty acid (LCFA) inhibition and trace metal (TM) deficiency. It evaluates current remedial strategies and the implementation of anaerobic membrane bioreactor (AnMBR) technology. It assesses the use of nitrogen-removed effluent return to dilute the influent for solving protein-rich dairy wastewater treatment. It explores the methodology of TM addition to dairy wastewater in accordance with microbial TM content and proliferation. It analyzes the multiple benefits of applying high-solid AnMBR to lipid-rich influent to mitigate LCFA inhibition. Finally, it proposes a promising low-carbon treatment system with enhanced bioenergy recovery, nitrogen removal, and simultaneous phosphorus recovery that could promote carbon neutrality for dairy industry wastewater treatment.

Mixed culture chain elongation for consumption of acetate and ethanol in anaerobic fermentation: The impact of salt type, dosage and acclimation

Microbial chain elongation is a newly developed carboxylate platform-based bioprocess, which often encounters high salinity stress due to saline feedstock and pH adjustment. In this study, we systematically investigated the effects of salt types (Na⁺, K⁺, and NH₄⁺), dosage, and salinity acclimation on microbial chain elongation, and identified the microbial community by high throughput 16S rRNA gene sequencing. The results showed that a high level of Na⁺ and NH₄⁺ (12.5 g/L of cations) exerted seriously inhibitory effects without chain elongating activity, while K⁺ had the slightest inhibition only with a little longer lag phase and lower products yield. The chain elongating products yields and the selectivity of caproate decreased with the increasing Na⁺ concentration, and 8.6 g/L of Na⁺ was found to be the threshold value for un-acclimated inoculum used for chain elongation. The acclimation to high saline conditions greatly promoted the consumption of acetate and ethanol with a shorter lag phase, and recovered a robust elongating activity for butyrate production. Furthermore, the high throughput 16S rRNA gene sequencing analysis results indicated that six genera, such as Clostridium IV and Clostridium sensu stricto, closely relating chain elongation process were depressed by high salinity, and the salinity acclimation helped to enrich the functional microbes. These findings could provide useful information for engineering microbial chain elongation process under saline conditions.